1. Field of the Invention
The present invention relates to an image reading apparatus having plural point light sources arranged in a straight line state and an image reading apparatus having the light reading apparatus.
2. Description of the Related Art
As an image reading apparatus used for an image forming apparatus such as a copying machine, one having a structure where plural LEDs (point light sources) lighting a document are arranged in a straight line state is known conventionally. See Japanese Patent Application Laid-Open Publication Nos. 07-162586 and 10-322521, for example. Furthermore, in a case where plural LEDs are used as light sources, in order to prevent the generation of illuminance ripple (unevenness of illumination distribution) in an arrangement direction of the LEDs at an object to be lighted, namely the document, a light leading member made of transparent resin, glass, or the like is arranged between the object to be lighted and the point light sources. The light leading member leads light irradiating from the point light sources and diffusing in a circle toward a surface of the document along a main scanning direction at the time when the document is read out, so that the light leading member can prevent the generation of the illuminance ripple.
However the inventions disclosed in the above-mentioned Japanese Patent Application Laid-Open Publications and others have a problem in that the surface of the document cannot be uniformly illuminated along the main scanning direction if a distance between the plural LEDs and the light leading member is not constant.
A state where the surface of the document is not being uniformly illuminated along the main scanning direction due to the distance between the LEDs and the light leading member not being constant is discussed with reference to FIG. 1 through FIG. 3. The lighting device of this optical reading apparatus, as shown in FIG. 1, includes an LED array substrate 102 and a light leading member 103. In the LED array substrate 102, plural LEDs (point light sources) 100 are arranged and fixed on a substrate 101. The light leading member 103 is positioned in front of an outputting direction of light output from the LED 100. The LED array substrate 102 and the light leading member 103 are attached to a housing member 104.
The light output from the LEDs 100 is led by the light leading member 103 so as to be irradiated along the main scanning direction of the document D provided on a contact glass 105. Reflection light from the document D is read out at a CCD (photoelectric conversion element) via a mirror 106 or lens (not shown) so that image information corresponding to the image of the document D can be obtained.
FIG. 2 shows a case where a position relationship between the light leading member 103 and the LED array substrate 102 is shifted from a proper position. The direction of the shift causes the distance between the LEDs and the light leading member 103 to be not constant. In this case, an amount of light, incident on the light leading member 103 after the light is output from the LEDs 100 at the position where the distance between the light leading member 103 and the LED 100 is short is large. The amount of light, incident on the light leading member 103 after the light is output from the LEDs 100 at the position where the distance between the light leading member 103 and the LED 100 is long is small. Because of this, an amount of light, incident on the document D after the light is output from the light leading member 103 at a side where the distance between the light leading member 103 and the LED 100 is short is large. An amount of light incident on the document D after the lights is output from the light leading member 103 at a side where the distance between the light leading member 103 and the LED 100 is long is small. Arrows shown in FIG. 2 show light beams incident on the document D and led by the light leading member 103 after the light beams are output from the corresponding LEDs 100. A length of each arrow represents an amount of the irradiated light.
FIG. 3 shows a case where a position relationship between the light leading member 103 and the LED array substrate 102 is shifted from a proper position.
A direction of the shift causes the arrangement direction of the LEDs 100 and the longitudinal direction of the light leading member 103 to be twisted. In this case, the light beams output from the LEDs arranged in the center of the arrangement direction are incident on the light leading part 103, led by the light leading member 103, and incident on the document D. However, the light beams output from the LEDs 100 positioned at both end sides in the arrangement direction are not incident in the light leading member 103. The document D is not lighted at either end side in a longitudinal direction of the light leading member 103.